Making lithographic printing plates

ABSTRACT

A thermally-sensitive, positive-working lithographic printing plate precursor can be used to prepare lithographic printing plates using high pH, silicate-free processing solutions. The precursor has a grained an anodized aluminum-containing substrate including a poly(vinyl phosphonic acid) interlayer. A first ink receptive layer, and optionally a second ink receptive layer, is disposed directly on the poly(vinyl phosphonic acid) interlayer. This first ink receptive layer comprises an aromatic acid dye that comprises at least two aromatic groups in an amount of least 0.5 weight %. In addition, the precursor comprises an infrared radiation absorber in one of the layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 13/602,367,filed Sep. 4, 2012, which is incorporated herein by reference in itsentirety and now granted as U.S. Pat. No. 8,936,899.

This application has related subject matter to U.S. patent applicationSer. No. 13/711,648, filed Dec. 12, 2012 (now issued as U.S. Pat. No.8,530,141), which is a Continuation-in-part of U.S. patent applicationSer. No. 12/606,378, filed Oct. 27, 2009 (now abandoned).

FIELD OF THE INVENTION

This invention relates to imaging and processing positive-workinglithographic printing plate precursors that have a unique acid dye inthe layer adjacent to the substrate, using infrared radiation to providelithographic printing plates.

BACKGROUND OF THE INVENTION

In conventional or “wet” lithographic printing, ink receptive regions,known as image areas, are generated on a hydrophilic surface. When thesurface is moistened with water and ink is applied, the hydrophilicregions retain the water and repel the ink, and the ink receptiveregions accept the ink and repel the water. The ink is transferred tothe surface of a material upon which the image is to be reproduced. Forexample, the ink can be first transferred to an intermediate blanketthat in turn is used to transfer the ink to the surface of the materialupon which the image is to be reproduced.

Imageable elements (lithographic printing plate precursors) useful toprepare lithographic printing plates typically comprise one or moreimageable layers applied over the hydrophilic surface of a substrate.The imageable layers include one or more radiation-sensitive componentsthat can be dispersed in a suitable binder. Alternatively, theradiation-sensitive component can also be the binder material. Followingimaging, either the imaged regions or the non-imaged regions of theimageable layer are removed by a suitable developer, revealing theunderlying hydrophilic surface of the substrate. If the imaged regionsare removed, the imageable element is considered as positive-working.Conversely, if the non-imaged regions are removed, the imageable elementis considered as negative-working. In each instance, the regions of theimageable layer (that is, the image areas) that remain areink-receptive, and the regions of the hydrophilic surface revealed bythe developing process accept water and aqueous solutions, typically afountain solution, and repel ink.

Direct digital or thermal imaging has become increasingly important inthe printing industry because of their stability to ambient light. Thelithographic printing plate precursors used for the preparation oflithographic printing plates have been designed to be sensitive to heator infrared radiation and can be exposed using thermal heads or moreusually, infrared laser diodes that image in response to signals from adigital image in a computer a platesetter. This “computer-to-plate”technology has generally replaced the former technology where maskingfilms were used to image the elements.

These imaging techniques often require the use of water or a developer(neutral to alkaline pH) as a processing solution to remove exposed(positive-working) or non-exposed (negative-working) regions of theimaged layer(s). In general, the processing solution is specificallydesigned for the specific radiation-sensitive chemistry in the imagedprecursor even though there is a general desire in the industry todesign one processing solution that can be used with much differentimaging chemistry.

Contrast dyes are often incorporated in precursor imaging layerformulations in order to provide a color for easy precursor handling andenabling inspection of defects during manufacturing. The color from acontrast dye serves an important function in the pre-press readabilityof dots for calibrations and in the printing press room to recognizeregister marks for precise fitting on the printing press. Inpositive-working lithographic printing plate precursors, bothsingle-layered and double-layered precursors, contrast dyes often servethe additional function of causing inhibition of the imaging formulationto developer attack and thereby stabilizing the dots in the resultingimage. However, a significant problem has been encountered with the useof highly colored contrast dyes. They can cause “staining” of thenon-imaged regions after development (processing).

One way to reduce this post-processing staining is to apply aninterlayer on the aluminum substrate before the image layerformulation(s) are applied. An interlayer that is commonly used ispoly(vinyl phosphonic acid) (PVPA) that can be applied either as a sprayor in a coating bath process. For many processing methods that use lowpH developers or high pH, silicate-containing developers, the presenceof the PVPA interlayer is sufficient to avoid staining from the contrastdyes.

However, when high pH, non-silicate-containing developers are used toprocess some positive-working imaging formulations comprising a strongcontrast dye, high staining can occur after development. One approach tosolving this problem has been to use an alternative interlayer (insteadof the PVPA interlayer). For example, some in the industry haveincorporated an interlayer formed from a phosphate/fluoride (PF) processto reduce staining.

However, the use of this phosphate/fluoride process is undesirablebecause of the hazardous materials used or formed (HF and cryolith) inthe process. In addition, considerable expense is required to installthe equipment necessary to use the phosphate/fluoride process and suchequipment requires additional space in the manufacturing facility,adding further costs.

There is a need to find useful contrast dyes for positive-workinglithographic printing plate precursors that cause no staining when PVPAinterlayers are used on the substrates and when the imaged precursorsare processed using a high pH, non silicate developer.

SUMMARY OF THE INVENTION

Positive-working lithographic printing plate precursors useful in thepresent invention comprise:

-   -   a grained and anodized aluminum-containing substrate,    -   a poly(vinyl phosphonic acid) interlayer disposed directly on        the grained and anodized aluminum substrate,    -   a first ink receptive layer that is disposed directly on the        poly(vinyl phosphonic acid) interlayer, the first ink receptive        layer comprising at least one water-insoluble, alkali        solution-soluble or -dispersible resin, and an aromatic acid dye        that comprises at least two aromatic groups and that is present        in an amount of least 0.5 weight %, based on the total dry        weight of the first receptive layer,    -   wherein each aromatic group has at least one anionic group        selected from the group consisting of carboxylate, sulfonate,        phenolate, and phosphonate groups,    -   the positive-working lithographic printing plate precursor being        infrared radiation-sensitive and further comprising an infrared        radiation absorber in either the first ink receptive layer or in        an optional second ink receptive layer that is disposed over the        first ink receptive layer, or in both of the first and second        ink receptive layers.

The present invention provides a method for forming a lithographicprinting plate, comprising:

-   -   imagewise exposing the positive-working lithographic printing        plate precursor of any embodiments described herein with        infrared radiation to form an imaged precursor comprising        exposed regions and non-exposed regions in the first ink        receptive layer and the second ink receptive layer, if present,        and    -   processing the imaged precursor to remove the exposed regions of        the first ink receptive layer and of the second ink receptive        layer, if present, using a silicate-free processing solution        having a pH of at least 12.5 and up to and including 14.

The present invention provides a positive-working lithographic printingplate precursor that exhibits reduced staining when a poly(vinylphosphonic acid) (PVPA) interlayer is incorporated on the substrate andunder the one or more imageable or ink receptive layers. Thisimprovement is particularly evident when the imaged precursors areprocessed using high pH, silicate-free processing solutions.

These advantages are achieved by using certain aromatic acid dyes in oneor more imageable layers in the precursor. These aromatic acid dyes areparticularly useful when incorporated into the imageable or inkreceptive layer that is closest to the PVPA interlayer. It has beenfound that these aromatic acid dyes can provide desired color contrastwhile reducing stain that can occur from development (processing) usingsilicate-free, high pH processing solutions.

DETAILED DESCRIPTION OF THE INVENTION Definitions

As used herein to define various components of the positive-workinglithographic printing plate precursors, processing solutions, inkreceptive compositions, formulations, and layers, unless otherwiseindicated, the singular forms “a,” “an,” and “the” are intended toinclude one or more of the components (that is, including pluralityreferents).

Each term that is not explicitly defined in the present application isto be understood to have a meaning that is commonly accepted by thoseskilled in the art. If the construction of a term would render itmeaningless or essentially meaningless in its context, the term'sdefinition should be taken from a standard dictionary.

The use of numerical values in the various ranges specified herein,unless otherwise expressly indicated otherwise, are considered to beapproximations as though the minimum and maximum values within thestated ranges were both preceded by the word “about.” In this manner,slight variations above and below the stated ranges can be used toachieve substantially the same results as the values within the ranges.In addition, the disclosure of these ranges is intended as a continuousrange including every value between the minimum and maximum values.

Unless the context indicates otherwise, when used herein, the terms“lithographic printing plate precursor,” “positive-working lithographicprinting plate precursor,” and “precursor” are meant to be references toembodiments of the present invention.

The term “support” is used herein to refer to an aluminum-containingmaterial (web, sheet, foil, or other form) that is then treated toprepare a “substrate” that refers to the hydrophilic article upon whichvarious ink receptive layers are disposed.

The term “post-treatment” refers to treating the grained and anodizedaluminum-containing support with an aqueous solution to coat it with apoly(vinyl phosphonic acid) interlayer formulation on the grained andanodized aluminum-containing substrate. Such a “post-treatment” is usedin the practice of the present invention before any ink receptive layerformulations are applied.

The precursors can be “single-layer precursors” comprising a single inkreceptive (or imageable) layer that is identified as the first inkreceptive layer. Alternative precursors can be “double-layer precursors”having two ink receptive layers identified as a first receptive layernearest the substrate and a second ink receptive layer that is disposedover the first receptive layer. In some literature, the first inkreceptive layer is known as the “inner” or inside imageable layer, andthe second ink receptive layer is known as the “outer” or outsideimageable layer.

The term “ink receptive,” as applied to the layers in the precursors,refers to a coating or layer material to which, after lithographicprinting plate after imaging and development, lithographic ink isattracted.

Unless otherwise indicated, percentages refer to percents by dry weightof a composition or layer, or % solids of a solution or formulation.

As used herein, the term “infrared” refers to radiation having a λ_(max)of at least 700 nm and higher. In most instances, the term “infrared” isused to refer to the “near-infrared” region of the electromagneticspectrum that is defined herein to be at least 700 nm and up to andincluding 1400 nm.

For clarification of definitions for any terms relating to polymers,reference should be made to “Glossary of Basic Terms in Polymer Science”as published by the International Union of Pure and Applied Chemistry(“IUPAC”), Pure Appl. Chem. 68, 2287-2311 (1996). However, anydefinitions explicitly set forth herein should be regarded ascontrolling.

Unless otherwise indicated, the terms “polymer” and “polymeric” refer tohigh and low molecular weight polymers including oligomers and includeshomopolymers and copolymers.

The term “copolymer” refers to polymers that are derived from two ormore different monomers, in random order along the polymer backbone.That is, they comprise recurring units having different chemicalstructures.

The term “backbone” refers to the chain of atoms in a polymer to which aplurality of pendant groups can be attached. An example of such abackbone is an “all carbon” backbone obtained from the polymerization ofone or more ethylenically unsaturated polymerizable monomers. However,other backbones can include heteroatoms wherein the polymer is formed bya condensation reaction or some other means.

Positive-Working Lithographic Printing Plate Precursors

Aromatic Acid Dyes:

The aromatic acid dyes useful in the present invention are located inthe first ink receptive layer of the precursor and each one comprises atleast two aromatic groups, and generally have two or more carboxylate,sulfonate, phenolate, or phosphonate groups. Each aromatic nucleus hasat least one of such acidic groups. Aromatic dyes comprising two or moresulfonate or carboxylate, or both carboxylate and sulfonate groups, areparticularly useful.

Useful classes of aromatic acid dyes include but are not limited to,acidic bis-azo dyes (such as Naphthol blue black and Trypan blue),acidic tris-azo dyes (such as Direct Blue 71), acidic triphenyl methanedyes (such as methyl blue, alumion, and Eosin Y), the acidity of whicharises from acid group substituents such as sulfonic acid groups. Anyamino group substituents present on the aromatic groups are eitherprimary amino groups or secondary amino groups (and not tertiary aminogroups) for example as in anthraquinone dyes (such as Alizarin BlueBlack B). Some useful aromatic acid dyes are demonstrated below in theInvention Examples.

These aromatic acid dyes also provide contrast between imaged andnon-imaged regions of the first receptive layer, and can also thus serveas “contrast” dyes in the precursor. As such, the aromatic acid dyesgenerally have an absorption peak of at least 400 nm to and including700 nm.

One or more aromatic acid dyes are present in the first ink receptivelayer in an amount of at least 0.2 weight % and generally up to andincluding 10 weight %, or typically at least 0.5 weight % and up to andincluding 5 weight %, all based on the total dry weight of the first inkreceptive layer.

In general, the first ink receptive layer comprising the one or morearomatic acid dyes is substantially free of basic dyes having anabsorption peak of at least 400 nm and up to and including 700 nm. By“substantially free” is meant that such basic dyes are present in anamount of less than 0.1 weight %, based on the total dry weight of thefirst ink receptive layer.

Grained and Anodized Aluminum-Containing Substrate:

In general, the lithographic printing plate precursors are formed bysuitable application of one or more ink receptive layer compositions toa suitable aluminum-containing substrate to form one or more inkreceptive layers. This aluminum-containing substrate is usually treatedor coated in various ways as described below prior to application of theformulation(s). For example, the aluminum-containing substrate istreated to provide an “interlayer” for improved adhesion orhydrophilicity, and the first ink receptive layer and optional secondink receptive layer, is applied over the interlayer.

The aluminum-containing substrate generally has a hydrophilic surface,or a surface that is more hydrophilic than the applied ink receptivelayer formulation on the imaging side. The aluminum-containing substratecomprises an aluminum support that is coated or treated using physicalgraining, electrochemical graining and chemical graining, followed byanodizing using a suitable acid to provide the desired anodic oxidesurface and a desired oxide pore diameter. The aluminum sheet ismechanically or electrochemically grained and anodized using phosphoricacid or sulfuric acid and conventional procedures. Anodization can becarried out using any suitable technique that provides these properties,but in many embodiments, the present invention comprises providing aphosphoric acid anodized aluminum substrate comprising the average oxidepore diameter of at least 15 nm and up to and including 80 nm.

Alternatively, the aluminum support can be anodized with sulfuric acidto obtain the desired anodic oxide pore size. For example, anelectrochemically grained aluminum support can be anodized in analternating current passing through a sulfuric acid solution (5-30weight %) at a temperature of at least 20° C. and up to and including60° C. for at least 5 seconds and up to and including 250 seconds toform an oxide layer on the metal surface. Generally, sulfuric acidanodization is carried out to provide an aluminum oxide layer of atleast 0.3 g/m² and typically at least 1 g/m² and up to and including 10g/m², or up to and including 5 g/m².

The sulfuric acid formed aluminum oxide layer generally has fine concaveparts that are sometimes referred to as “micropores” or “pores” that aredistributed, perhaps uniformly, over the layer surface. The density (orvacancy) is generally controlled by properly selecting the conditions ofthe sulfuric acid anodization treatment. The pores can appear as columnswithin the aluminum oxide layer, as viewed in a cross-sectionalmicroimage. These columnar pores can have an average diameter of lessthan 20 nm before they are treated to widen the average diameter at theoutermost surface, or most of the columnar pores have an averagediameter of at least 5 nm and up to and including 20 nm before they aretreated.

The electrochemically grained and sulfuric acid anodizedaluminum-containing support can be treated to widen the pores in thealuminum oxide layer (“pore-widening treatment”) so that the diameter ofthe columnar pores at their outermost surface (that is, nearest theoutermost layer surface) is at least 90%, and more typically at least92%, and even more than 100% of the average diameter of the columnarpores. The average diameter of the columnar pores can be measured usinga field emission scanning electron microscope. Once this averagediameter is determined, it is possible to determine whether the diameterat the outermost surface is at least 90% of that average diameter valueusing similar measuring techniques.

The columnar pores can be widened using an alkaline or acidicpore-widening solution to remove at least 10 weight % and up to andincluding 80 weight %, typically at least 10 weight % and up to andincluding 60 weight %, or more likely at least 20 weight % and up to andincluding 50 weight %, of the original aluminum oxide layer. Porewidening can thus be accomplished using an alkaline solution containingsodium hydroxide, potassium hydroxide, lithium hydroxide, or mixtures ofhydroxides, having a pH of at least 11 and up to and including 13, ormore likely having a pH of at least 11.5 and up to and including 12.5,and a hydroxide (such as a sodium hydroxide) concentration of at least0.15 g/l and up to and including 1.5 g/l. The alkaline or acidicpore-widening solution generally has conductivity of at least 0.8 mS/cmand up to and including 8.2 mS/cm.

Alternatively, one can use an acidic solution containing an inorganicacid such as sulfuric acid, phosphoric acid, hydrochloric acid, nitricacid, or mixtures of these acids at a concentration of at least 10 g/land up to and including 500 g/l, or more likely of at least 20 g/l, andup to and including 100 g/l.

Particularly useful pore-widening solutions comprise sodium hydroxide,potassium hydroxide, sulfuric acid, hydrochloric acid, nitric acid, orphosphoric acid.

The pore-widening treatment with the acidic or alkaline solution can becarried out by contacting the electrochemically grained and sulfuricacid anodized support, for example by immersion in the solution, for atleast 3 seconds and up to and including 300 seconds, and typically forat least 10 seconds and up to and including 120 seconds to providecolumnar pores having an average diameter of at least 15 nm and up toand including 80 nm. The treatment temperature is at least 0° C. and upto and including 110° C. or typically a treatment temperature of atleast 20° C. and up to and including 70° C.

Further details of these sulfuric acid anodizing and pore wideningprocesses are provided in copending and commonly assigned U.S. Pat. No.8,722,308, (filed Aug. 31, 2011 by Hayashi) that is incorporated hereinby reference.

Alternative anodic pore treatment is described in U.S. Pat. No.6,890,700 (Tomita et al.) that is incorporated herein by reference. Thispublication describes treatment of the anodic oxide layer on thealuminum-containing substrate so that pore opening diameter is differentthan the pore diameter away from the surface.

An interlayer is formed by treatment of the grained and anodizedaluminum-containing support with an aqueous solution of poly(vinylphosphonic acid) (PVPA) to provide a poly(vinyl phosphonic acid)interlayer. This interlayer formulation can be formed by dissolvingpoly(vinyl phosphonic acid) in water in an amount of at least 0.05weight % and up to and including 20 weight %. The formulation can alsoinclude optional components such as phosphoric acid, poly(acrylic acid),and copolymers derived in part from vinyl phosphonic acid. Theinterlayer formulation is applied using any suitable manner and dried toprovide a layer having a dry coverage of at least 10 mg/m² and up to andincluding 200 mg/m².

The thickness of the grained and anodized aluminum-containing substrate(with interlayer) can be varied, but should be sufficient to sustain thewear from printing and thin enough to wrap around a printing form. Someembodiments include a grained and anodized aluminum-containing substratethat has a thickness of from at least 100 μm and up to and including 600μm.

The backside (non-imaging side) of the grained and anodizedaluminum-containing substrate can be coated with anon-radiation-sensitive slipping or matte layer to improve handling and“feel” of the lithographic printing plate precursor.

The grained and anodized aluminum-containing substrate can also be in acylindrical form having the poly(vinyl phosphonic acid) interlayer andimageable layer(s) disposed thereon, and thus be an integral part of theprinting press. The use of such imageable cylinders is described forexample in U.S. Pat. No. 5,713,287 (Gelbart) that is incorporated hereinby reference.

Single Layer Precursors:

Some embodiments of such positive-working lithographic printing plateprecursors comprise a single ink receptive layer directly disposed onthe interlayer on the grained and anodized aluminum-containingsubstrate. Other embodiments (described below) comprise a first inkreceptive layer disposed directly on the interlayer and a second inkreceptive layer disposed on the first ink receptive layer.

The lithographic printing plate precursors comprise one or more of thearomatic acid dyes in the first receptive layer, and optionally one ormore infrared radiation absorber within one or more water-insoluble,alkali solution-soluble or -dispersible resins (polymeric binders) that,upon suitable irradiation to infrared radiation, are soluble,dispersible, or removable in processing solutions described below. Thus,the first ink receptive layer, upon infrared radiation irradiation,undergoes a change in solubility properties with respect to theprocessing solution in its irradiated (exposed) regions.

Compositions of first ink receptive layers in positive-workinglithographic printing plate precursors are described for example, inU.S. Pat. No. 6,255,033 (Levanon et al.), U.S. Pat. No. 6,280,899(Parsons et al.), U.S. Pat. No. 6,391,524 (Yates et al.), U.S. Pat. No.6,485,890 (Parsons et al.), U.S. Pat. No. 6,558,869 (MNcCullough etal.), U.S. Pat. No. 6,706,466 (Lott et al.), U.S. Pat. No. 6,541,181(Levanon et al.), U.S. Pat. No. 7,223,506 (Kitson et al.), U.S. Pat. No.7,247,418 (Saraiya et al.), U.S. Pat. No. 7,270,930 (Hauck et al.), U.S.Pat. No. 7,279,263 (Goodin), and U.S. Pat. No. 7,399,576 (Levanon), andU.S. Published Patent Applications 2006/0130689 (Muller et al.),2005/0214677 (Nagashima), 2004/0013965 (Memetea et al.), 2005/0003296(Memetea et al.), and 2005/0214678 (Nagashima), all incorporated hereinby reference.

The first ink receptive layer can contain one or more phenolic polymericbinders that are generally water-insoluble but soluble in alkalineprocessing solutions (defined below) after infrared radiation imaging.In most embodiments of the lithographic printing plate precursors, thesepolymeric binders are present in the first ink receptive layer in anamount of at least 10 weight % and typically from at least 20 weight %and up to and including 80 weight % of the total dry first ink receptivelayer weight. The term “phenolic” means a hydroxyl-substituted phenylgroup.

Useful phenolic polymers include but are not limited to, poly(vinylphenols) or derivatives thereof. They can also include pendant acidicgroups such as carboxylic (carboxy), sulfonic (sulfo), phosphonic(phosphono), or phosphoric acid groups that are incorporated into thepolymer molecule or pendant to the polymer backbone. Other usefuladditional phenolic polymers include but are not limited to, novolakresins, resole resins, poly(vinyl acetals) having pendant phenolicgroups, and mixtures of any of these resins (such as mixtures of one ormore novolak resins and one or more resole resins). Generally, suchresins have a number average molecular weight of at least 3,000 and upto and including 200,000, and typically at least 6,000 and up to andincluding 100,000, as determined using conventional procedures. Typicalnovolak resins include, but are not limited to, phenol-formaldehyderesins, cresol-formaldehyde resins, phenol-cresol-formaldehyde resins,p-t-butylphenol-formaldehyde resins, and pyrogallol-acetone resins, suchas novolak resins prepared from reacting m-cresol or an m,p-cresolmixture with formaldehyde using conventional conditions. For example,some useful novolak resins include, but are not limited to,xylenol-cresol resins, for example, SPN400, SPN420, SPN460, and VPN 1100(that are available from AZ Electronics) and EP25D40G and EP25D50G(noted below for the Examples) that have higher molecular weights, suchas at least 4,000.

Other useful additional resins in the first ink receptive layer includepolyvinyl compounds having phenolic hydroxyl groups, includepoly(hydroxystyrenes) and copolymers containing recurring units of ahydroxystyrene and polymers and copolymers containing recurring units ofsubstituted hydroxystyrenes. Also useful are branchedpoly(hydroxystyrenes) having multiple branched hydroxystyrene recurringunits derived from 4-hydroxystyrene as described for example in U.S.Pat. No. 5,554,719 (Sounik); and U.S. Published Patent Applications2003/0050191 (Bhatt et al.), 2005/0051053 (Wisnudel et al.), and2008/0008956 (Levanon et al.), all of which are incorporated herein byreference. For example, such branched hydroxystyrene polymers compriserecurring units derived from a hydroxystyrene, such as from4-hydroxystyrene, which recurring units are further substituted withrepeating hydroxystyrene units (such as 4-hydroxystyrene units)positioned ortho to the hydroxy group. These branched polymers can havea weight average molecular weight (M_(w)) of at least 1,000 and up toand including 30,000. In addition, they can have a polydispersity ofless than 2. The branched poly(hydroxystyrenes) can be homopolymers orcopolymers with non-branched hydroxystyrene recurring units.

Another group of useful polymeric binders in the first ink receptivelayer are poly(vinyl phenol) and derivatives thereof. Such polymers areobtained generally by polymerization of vinyl phenol monomers, that is,substituted or unsubstituted vinyl phenols. Some vinyl phenol copolymersare described in EP 1,669,803A (Barclay et al.).

The positive-working lithographic printing plate precursor also includesone or more infrared radiation absorbers in one or more ink receptivelayers, such as the first ink receptive layer in the single-layerprecursors. Such infrared radiation absorbers are sensitive tonear-infrared or infrared radiation, for example of at least 700 nm andup to and including 1400 nm and typically at least 750 nm and up to andincluding 1250 nm.

Some useful infrared radiation absorbers are sensitive to both infraredradiation (typically of at least 700 nm and up to and including 1400 nm)and visible radiation (typically of at least 450 nm and up to andincluding 700 nm), as described in U.S. Pat. No. 7,429,445 (Munnelly etal.) that is incorporated herein by reference.

Other useful infrared radiation absorbers include but are not limitedto, azo dyes, squarilium dyes, croconate dyes, triarylamine dyes,thioazolium dyes, indolium dyes, oxonol dyes, oxaxolium dyes, cyaninedyes, merocyanine dyes, phthalocyanine dyes, indocyanine dyes,indotricarbocyanine dyes, oxatricarbocyanine dyes, thiocyanine dyes,thiatricarbocyanine dyes, cryptocyanine dyes, naphthalocyanine dyes,polyaniline dyes, polypyrrole dyes, polythiophene dyes,chalcogenopyryloarylidene and bi(chalcogenopyrylo)polymethine dyes,oxyindolizine dyes, pyrylium dyes, pyrazoline azo dyes, oxazine dyes,naphthoquinone dyes, anthraquinone dyes, quinoneimine dyes, methinedyes, arylmethine dyes, squarine dyes, oxazole dyes, croconine dyes,porphyrin dyes, and any substituted or ionic form of the preceding dyeclasses. Suitable dyes are also described in U.S. Pat. No. 5,208,135(Patel et al.), U.S. Pat. No. 6,153,356 (Urano et al.), U.S. Pat. No.6,264,920 (Achilefu et al.), U.S. Pat. No. 6,309,792 (Hauck et al.),U.S. Pat. No. 6,569,603 (Furukawa), U.S. Pat. No. 6,787,281 (Tao etal.), U.S. Pat. No. 7,135,271 (Kawauchi et al.), and EP 1,182,033A2(noted above) all incorporated herein by reference. Infrared radiationabsorbing N-alkylsulfate cyanine dyes are described for example in U.S.Pat. No. 7,018,775 (Tao).

In addition to low molecular weight IR-absorbers, dyes having IR dyechromophores bonded to polymers can be used as well. Moreover, IR dyecations can be used as well, that is, the cation is the IR absorbingportion of the dye salt that ionically interacts with a polymercomprising carboxy, sulfo, phospho, or phosphono groups in the sidechains.

Near infrared absorbing cyanine dyes are also useful and are describedfor example in U.S. Pat. No. 6,309,792 (noted above), U.S. Pat. No.6,264,920 (noted above), U.S. Pat. No. 6,153,356 (noted above), and U.S.Pat. No. 5,496,903 (Watanabe et al.) that are incorporated herein byreference. Suitable dyes can be formed using conventional methods andstarting materials or obtained from various commercial sources includingAmerican Dye Source (Baie D'Urfe, Quebec, Canada) and FEW Chemicals(Germany). Other useful dyes for near infrared diode laser beams aredescribed in U.S. Pat. No. 4,973,572 (DeBoer).

Cyanine dyes having an anionic chromophore are also useful. For example,the cyanine dye can have a chromophore having two heterocyclic groups.In another embodiment, the cyanine dye can have from two sulfonic acidgroups, such as two sulfonic acid groups and two indolenine groups asdescribed for example in U.S Patent Application Publication No.2005-0130059 (Tao) that is incorporated herein by reference.

A general description of a useful class of suitable cyanine dyes isshown by the formula in [0026] of WO 2004/101280 (Munnelly et al.).

Useful infrared radiation absorbers can also be pigments includingcarbon blacks such as carbon blacks that are surface-functionalized withsolubilizing groups. Carbon blacks that are grafted to hydrophilic,nonionic polymers, such as FX-GE-003 (manufactured by Nippon Shokubai),or which are surface-functionalized with anionic groups, such asCAB-O-JET® 200 or CAB-O-JET® 300 (manufactured by the Cabot Corporation)are also useful. Other useful pigments include, but are not limited to,Heliogen Green, Nigrosine Base, iron (III) oxides, manganese oxide,Prussian Blue, and Paris Blue. The size of the pigment particles shouldnot be more than the thickness of the imageable layer and preferably thepigment particle size will be less than half the thickness of theimageable layer.

The one or more infrared radiation absorbers can be present in theprecursor in an amount generally of at least 0.5 weight % and up to andincluding 30 weight % and typically at least 3 weight % and up to andincluding 20 weight %, based on total solids of the ink receptive layerin which the compounds are located. The particular amount needed forthis purpose would be readily apparent to one skilled in the art.

In some embodiments, the infrared radiation absorber is present in thesingle ink receptive layer, identified as the first ink receptive layer.Alternatively or additionally, the infrared radiation absorbers can belocated in second ink receptive layer (described below).

The single-layer precursor can be prepared by applying the first inkreceptive layer formulation to the interlayer of the grained andanodized aluminum-containing substrate using conventional coating orlamination methods. Thus, the formulation can be applied by dispersingor dissolving the desired ingredients in a suitable coating solvent, andthe resulting formulation is applied to the interlayer of the grainedand anodized aluminum-containing substrate using suitable equipment andprocedures, such as spin coating, knife coating, gravure coating, diecoating, slot coating, bar coating, wire rod coating, roller coating, orextrusion hopper coating. The first ink receptive formulation can alsobe applied by spraying it onto an interlayer.

The dry coating weight for the first ink receptive layer can be at least0.5 g/m² to and including 2.5 g/m² and typically at least 1 g/m² to andincluding 2 g/m².

The selection of solvents used to coat the first ink receptive layerformulation depends upon the nature of the polymeric materials and othercomponents in the formulations, and can be coated out of acetone, methylethyl ketone or another ketone, tetrahydrofuran, 1-methoxypropan-2-ol,1-methoxy-2-propyl acetate, and mixtures thereof using conditions andtechniques well known in the art. The coated first ink receptive layercan be dried in a suitable manner.

Multi-Layer Positive-Working Precursors:

Other positive-working lithographic printing plate precursors of thisinvention are multi-layer precursors that comprise the noted grained andanodized aluminum-containing substrate, the first ink receptive layer(as described above for components, formulation amounts, and drycoverage), and a second ink receptive layer that generally serves as theoutermost layer, disposed over the first ink receptive layer. In mostembodiments, the second ink receptive layer is disposed directly on thefirst ink receptive layer.

Before thermal imaging, the second ink receptive layer is generally notsoluble or removable by an alkaline processing solution within the usualtime allotted for development, but after thermal imaging, the exposedregions of the second ink receptive layer are soluble in the processingsolution. In such instances, the first ink receptive layer is alsogenerally removable by the alkaline processing solution.

An infrared radiation absorber (described above) can also be present insuch multi-layer precursors. One or more infrared radiation absorberscan be in the first ink receptive layer, the second receptive layer, orboth of the first and second ink receptive layers. In still otherembodiments, there can be an intermediate layer between the first andsecond ink receptive layers, and this intermediate layer can alsoinclude an infrared radiation absorber layer but can optionally be in aseparate layer between the inner and outer layers.

The infrared radiation absorber can be present in the multi-layerprecursor in an amount of generally at least 0.5 weight % and up to andincluding 30 weight % and typically at least 3 weight % and up to andincluding 25 weight %, based on the total dry weight of the precursor.As noted above, the infrared radiation absorber can be located in one ormore layers and the amount of the infrared radiation absorber can beapportioned to the respective layers in a desired manner. The particularamount of a given compound to be used could be readily determined by oneskilled in the art.

Materials useful in thermally imageable, multi-layer positive-workinglithographic printing plate precursors are described, for example, inU.S. Pat. No. 6,294,311 (Shimazu et al.), U.S. Pat. No. 6,352,812(Shimazu et al.), U.S. Pat. No. 6,593,055 (Shimazu et al.), U.S. Pat.No. 6,352,811 (Patel et al.), U.S. Pat. No. 6,358,669 (Savariar-Hauck etal.), U.S. Pat. No. 6,528,228 (Savariar-Hauck et al.), U.S. Pat. No.7,163,770 (Saraiya et al.), U.S. Pat. No. 7,163,777 (Ray et al.), U.S.Pat. No. 7,186,482 (Kitson et al.), U.S. Pat. No. 7,223,506 (notedabove), U.S. Pat. No. 7,229,744 (Patel), U.S. Pat. No. 7,241,556(Saraiya et al.), U.S. Pat. No. 7,247,418 (noted above), U.S. Pat. No.7,291,440 (Ray et al.), U.S. Pat. No. 7,300,726 (Patel et al.), and U.S.Pat. No. 7,338,745 (Ray et al.), U.S. Patent Application Publications2004/0067432 A1 (Kitson et al.) and 2005/0037280 (Loccufier et al.), allincorporated herein by reference.

These multi-layer precursors are formed by suitable application of afirst ink receptive layer composition onto the interlayer describedabove, following by application of a second ink receptive layerformulation.

The second ink receptive layer generally comprises one or more resins orpolymeric binders that can be the same or different than the resins(polymeric binders) described above for the first ink receptive layer.The polymeric binders in the second ink receptive layer can be aphenolic polymeric binder as described above for the first ink receptivelayer.

The second ink receptive layer can also include one or more colorants asdescribed for example in U.S. Pat. No. 6,294,311 (noted above) that isincorporated herein by reference, including triarylmethane dyes such asethyl violet, crystal violet, malachite green, brilliant green, Victoriablue B, Victoria blue R, and Victoria pure blue BO. These compounds canact as contrast dyes that distinguish the non-exposed regions from theexposed regions in the imaged and developed precursor. The second inkreceptive layer can also optionally include other contrast dyes,printout dyes, coating surfactants, dispersing aids, humectants,biocides, viscosity builders, drying agents, defoamers, preservatives,and antioxidants.

The multi-layer precursors can be prepared by sequentially applying afirst ink receptive layer formulation onto the interlayer (describedabove), and then applying a second ink receptive layer formulation overthe first ink receptive layer (usually when dried) using conventionalcoating or lamination methods. It is important to avoid intermixing ofthe first and second ink receptive layer formulations.

Thus, the first and second ink receptive layers can be applied bydispersing or dissolving the desired ingredients for each layer in asuitable coating solvent, and the resulting formulations aresequentially or simultaneously applied to the substrate (with theinterlayer) using suitable equipment and procedures, such as spincoating, knife coating, gravure coating, die coating, slot coating, barcoating, wire rod coating, roller coating, or extrusion hopper coating.The ink receptive layer formulations can also be applied by sprayingonto the substrate (with the interlayer).

The selection of solvents used to coat both the first and second inkreceptive layers depends upon the nature of the polymeric binders andother components in the layer formulations. To prevent the first andsecond ink receptive layer formulations from mixing or the first inkreceptive layer from dissolving when the second ink receptive layerformulation is applied, the second ink receptive layer formulationshould be coated from a solvent in which the polymeric binder(s) in thefirst ink receptive layer is(are) insoluble.

Generally, the first ink receptive layer formulation is coated out of asolvent mixture of methyl ethyl ketone (MEK), 1-methoxy-2-propyl acetate(PMA), γ-butyrolactone (BLO), and water; a mixture of MEK, BLO, water,and 1-methoxypropan-2-ol (also known as Dowanol® PM or PGME); a mixtureof diethyl ketone (DEK), water, methyl lactate, and BLO; a mixture ofDEK, water, and methyl lactate; or a mixture of methyl lactate,methanol, and dioxolane.

The second ink receptive layer formulation can be coated out of solventsor solvent mixtures that do not dissolve the first ink receptive layer.Typical solvents for this purpose include but are not limited to, butylacetate, iso-butyl acetate, methyl iso-butyl ketone, DEK,1-methoxy-2-propyl acetate (PMA), iso-propyl alcohol, PGME and mixturesthereof.

After drying the layers, the lithographic printing plate precursors canbe further “conditioned” with a heat treatment of at least 40° C. and upto and including 90° C. for at least 4 hours (for example, at least 20hours) under conditions that inhibit the removal of moisture from thedried layers. During the heat treatment, the lithographic printing plateprecursors are wrapped or encased in a water-impermeable sheet materialto represent an effective barrier to moisture removal from theprecursors, or the heat treatment of the precursors is carried out in anenvironment in which relative humidity is controlled to at least 25%. Inaddition, the water-impermeable sheet material can be sealed around theedges of the precursors, with the water-impermeable sheet material beinga polymeric film or metal foil that is sealed around the edges of theprecursors.

In some embodiments, this heat treatment can be carried out with a stackcomprising at least 100 of the same lithographic printing plateprecursors, or when the precursor is in the form of a coil or web. Whenconditioned in a stack, the individual precursors can be separated bysuitable interleaving papers. The interleaving papers can be keptbetween the imageable elements after conditioning during packing,shipping, and use by the customer.

Imaging Conditions

During the method of this invention, the positive-working lithographicprinting plate precursor is exposed to a suitable source of exposinginfrared radiation depending upon the infrared radiation absorberpresent in the precursor to provide specific sensitivity that is at awavelength of at least 700 nm and up to and including 1500 nm, or morelikely of at least 750 nm and up to and including 1400 nm. Imagewiseexposing provides exposed regions and non-exposed regions in the firstink receptive layer and the second ink receptive layer, if present.

For example, imaging can be carried out using imaging or exposingradiation from an infrared radiation-generating laser (or array of suchlasers). Imaging also can be carried out using imaging infraredradiation at multiple infrared wavelengths at the same time if desired.The laser used to expose the lithographic printing plate precursor isusually a diode laser, because of the reliability and low maintenance ofdiode laser systems, but other lasers such as gas or solid-state laserscan also be used. The combination of power, intensity, and exposure timefor laser imaging would be readily apparent to one skilled in the art.

The imaging apparatus can be configured as a flatbed recorder or as adrum recorder, with the lithographic printing plate precursor mounted tothe interior or exterior cylindrical surface of the drum. An example ofa useful imaging apparatus is available as models of Kodak® Trendsetterplatesetters available from Eastman Kodak Company that contain laserdiodes that emit near infrared radiation at a wavelength of about 830nm. Other suitable imaging sources include the Crescent 42T Platesetterthat operates at a wavelength of 1064 nm (available from GerberScientific, Chicago, Ill.) and the Screen PlateRite 4300 series or 8600series platesetter (available from Screen USA, Chicago, Ill.) thatoperates at a wavelength of 810 nm.

Imaging with infrared radiation can be carried out generally at imagingenergies of at least 30 mJ/cm² and up to and including 500 mJ/cm² andtypically at least 50 mJ/cm² and up to and including 300 mJ/cm²depending upon the sensitivity of the imageable layer. With theseplatesetters, any imaging parameters, such as the “surface depth”parameter of a Magnus 800 platesetter (Eastman Kodak Company) or the“focus” parameter of a PlateRite 4300 platesetter (Dainippon ScreenCompany), are decided by observing the difference in contrast betweenexposed regions and non-exposed regions in a stepwise imaging process.By using stepwise imaged lithographic printing plate precursor, ashortened printing run is possible and the obtained prints are alsouseful for determining such imaging parameters.

Development and Printing

After imaging, the imaged lithographic printing plate precursors can beprocessed “off-press” using a suitable processing solution describedbelow. When the positive-working lithographic printing plate precursorsare imaged and processed, the imaged (exposed) regions in the first inkreceptive layer (and second ink receptive layer if present) are removedduring processing while the non-exposed regions remain, revealing thegrained and anodized aluminum-containing substrate (as well asinterlayer).

Development off-press can be accomplished using what is known as“manual” development, “dip” development, or processing with an automaticdevelopment apparatus (processor). In the case of “manual” development,development is conducted by rubbing the entire imaged precursor with asponge or cotton pad sufficiently impregnated with a suitable processingsolution (described below), and followed by rinsing with water. “Dip”development involves dipping the imaged precursor in a tank or traycontaining the appropriate processing solution for at least 10 secondsand up to and including 60 seconds (especially at least 20 seconds andup to and including 40 seconds) under agitation, followed by rinsingwith water with or without rubbing with a sponge or cotton pad. The useof automatic development apparatus is well known and generally includespumping a developer or processing solution into a developing tank orejecting it from spray nozzles. The imaged precursor is contacted withthe processing solution in an appropriate manner. The apparatus can alsoinclude a suitable rubbing mechanism (for example a brush or roller) anda suitable number of conveyance rollers. Some developing apparatusinclude laser exposure means and the apparatus is divided into animaging section and a developing section.

Thus, the processing solution (or developer) can be applied to theimaged precursor by rubbing, spraying, jetting, dipping, immersing, slotdie coating (for example see FIGS. 1 and 2 of U.S. Pat. No. 6,478,483 ofMaruyama et al.) or reverse roll coating (as described in FIG. 4 of U.S.Pat. No. 5,887,214 of Kuriu et al.), or by wiping the outermost layerwith the processing solution or contacting it with a roller, impregnatedpad, or applicator. For example, the imaged precursor can be brushedwith the processing solution, or it can be poured onto or applied byspraying the imaged surface with sufficient force to remove thenon-exposed regions using a spray nozzle system (spray bar) as describedfor example in [0124] of EP 1,788,431A2 and U.S. Pat. No. 6,992,688(Shimazu et al.). As noted above, the imaged precursor can be immersedin the processing solution and rubbed by hand or with an apparatus. Toassist in the removal of the back side coating, a brush roller or othermechanical component can be placed in contact with the back side coatingduring processing.

The processing solution can also be applied in a processing unit (orstation) in a suitable apparatus that has at least one roller forrubbing or brushing the imaged precursor while the processing solutionis applied. Residual processing solution can be removed (for example,using a squeegee or nip rollers) or left on the resulting lithographicprinting plate without any rinsing step. Excess processing solution canbe collected in a tank and used several times, and replenished ifnecessary from a reservoir. The processing solution replenisher can beof the same concentration as that used in processing, or be provided inconcentrated form and diluted with water at an appropriate time.

Such processing can be carried out after imagewise exposing thepositive-working lithographic printing plate precursor of this inventionthat can have a single first ink receptive layer that is disposed overthe poly(vinyl phosphonic acid) interlayer, or that can have both firstand second ink receptive layers disposed over the noted interlayer, andin which an infrared radiation absorber is present in the first inkreceptive layer in an amount of at least 0.5 weight %, based on thefirst ink receptive layer total dry weight. Such precursors can includethe aromatic acid dye in the first ink receptive layer.

Both aqueous alkaline developers and organic solvent-containingdevelopers or processing solutions can be used in the practice of thisinvention. Some useful processing solutions are described for example,in U.S. Pat. No. 7,507,526 (Miller et al.) and U.S. Pat. No. 7,316,894(Miller et al.) that are incorporated herein by reference. Usefulalkaline aqueous processing solutions (developers) include 3000Developer, 9000 Developer, GOLDSTAR Developer, GREENSTAR Developer,ThermalPro Developer, PROTHERM Developer, MX1813 Developer, and MX1710Developer (all available from Eastman Kodak Company). These processingcompositions also generally include surfactants, chelating agents (suchas salts of ethylenediaminetetraacetic acid), and alkaline components(such as inorganic metasilicates, organic metasilicates, hydroxides, andbicarbonates).

Organic solvent-containing processing solutions (developers) aregenerally single-phase processing solutions of one or more organicsolvents that are miscible with water. Useful organic solvents includethe reaction products of phenol with ethylene oxide and propylene oxide[such as ethylene glycol phenyl ether (phenoxyethanol)], benzyl alcohol,esters of ethylene glycol and of propylene glycol with acids having 6 orless carbon atoms, and ethers of ethylene glycol, diethylene glycol, andof propylene glycol with alkyl groups having 6 or less carbon atoms,such as 2-ethylethanol and 2-butoxyethanol. The organic solvent(s) isgenerally present in an amount of from about 0.5 weight % and up to 15weight % based on total processing solution weight. The organicsolvent-containing developers can be neutral, alkaline, or slightlyacidic in pH, and typically, they are alkaline in pH. Representativeorganic solvent-containing developers include ND-1 Developer, Developer980, Developer 1080, 2 in 1 Developer, 955 Developer, D29 Developer(described below), and 956 Developer (all available from Eastman KodakCompany).

Particularly useful processing solutions have a pH of at least 12 and upto and including 14, or more likely at least 12 and up to and including13.7, or at least 12.5 and up to and including 14, and particularly whensuch processing solutions are “silicate-free,” meaning that they containless than 1 weight % of silicates and metasilicates, based on totalprocessing solution weight.

Particularly useful silicate-free processing solutions are described inU.S. Patent Application Publication No. 2012/0125216 (Levanon et al.)that is incorporated herein by reference. Such silicate-free processingsolutions generally have a pH of at least 12, and typically at least 12and up to and including 14, or more likely at least 12.5 and up to andincluding 14. This highly alkaline pH is generally provided using one ormore alkali agents other than silicates and metasilicates. Useful alkaliagents include alkali metal hydroxides such as sodium hydroxide andpotassium hydroxide. Potassium ions can be more prevalent than thesodium ions and the total amount of the alkali metal ions is generallyat least 0.3 gram-atom/kg and up to and including 1 gram-atom/kg.

These silicate-free processing solutions can also include one or moremetal cations (M²⁺) that are generally selected from the groupconsisting of barium, calcium, strontium, and zinc cation. Calcium,strontium, and zinc cations are particularly useful. The metal cationsM²⁺ are generally present in the processing solutions in an amount of atleast 0.001 gram-atom/kg, and typically at least 0.001 gram-atom/kg andup to and including 0.01 gram-atom/kg.

The silicate-free processing solutions can also include one or morechelating agents, each of which has a complex formation constant (log K)for the M²⁺ metal cation of at least 3.5 and less than or equal to 4.5,and a log K for aluminum ion that is 7 or less. Useful chelating agentswith these properties include but are not limited to,phosphono-polycarboxylic acids such as phosphonoalkyl polycarboxylicacids, such as 2-phosphonobutane-1,2,4-tricarboxylic acid, which isparticularly useful with calcium metal cations. The described chelatingagents can be present in an amount of at least 0.01 mol/liter and up toand including 0.1 mol/liter, or typically at least 0.03 mol/liter and upto and including 0.1 mol/liter.

A cationic surfactant or a betaine can also be present in thesilicate-free processing solutions in an amount of at least 0.01 weight% and typically at least 0.1 weight % and up to and including 3 weight%. Suitable cationic surfactants for use in the present inventioninclude, but are not limited to, quaternary ammonium halides of fattyacids such as a fatty acid quaternary ammonium chloride. One example ofsuch cationic surfactants is provided in Hydromax 300 (ChemaxPerformance Products, Greenville, S.C.) that is described for example,in U.S. Patent Application Publication No. 2006/0154187 (Wilson et al.)that is incorporate herein by reference.

The silicate-free processing solutions can also comprise one or moresurfactants to achieve the best wetting, stabilizing, solubilizing,protecting, dispersing, and rinsing properties. Such surfactants aregenerally anionic or nonionic in nature. Useful anionic surfactants areof the alkyaryl sulfonate class, such as an alkylaryl sulfonate, forexample, alkyldiphenyloxide disulfonate that is available as Dowfax® 2A1from Dow Chemical Co. The anionic and nonionic surfactants can bepresent in an amount of at least 0.1 weight % and up to and including 2weight %.

Although each processing solution can also be used as its ownreplenisher, in addition, a specially formulated replenisher can beused. In the replenisher composition, the concentration of alkali agentis generally higher than the concentration of the alkali agent in theworking strength processing solution, to compensate for the consumptionof the alkali agent during the development process.

Following off-press development, the resulting lithographic printingplate can be postbaked with or without blanket or floodwise exposure toUV or visible radiation. Alternatively, a blanket UV or visibleradiation exposure can be carried out, without a postbake operation.

Printing can be carried out by putting the imaged and developedlithographic printing plate on a suitable printing press. Thelithographic printing plate is generally secured in the printing pressusing suitable clamps or other holding devices. Once the lithographicprinting plate is secured in the printing press, printing is carried outby applying a lithographic printing ink and fountain solution to theprinting surface of the lithographic printing plate. The fountainsolution is taken up by the surface of the hydrophilic substraterevealed by the imaging and processing steps, and the ink is taken up bythe remaining regions of the outermost ink receptive layer. The ink isthen transferred to a suitable receiving material (such as cloth, paper,metal, glass, or plastic) to provide a desired impression of the imagethereon. If desired, an intermediate “blanket” roller can be used totransfer the ink from the lithographic printing plate to the receivingmaterial (for example, sheets of paper). The lithographic printingplates can be cleaned between impressions, if desired, usingconventional cleaning means.

The present invention provides at least the following embodiments andcombinations thereof, but other combinations of features are consideredto be within the present invention as a skilled artisan would appreciatefrom the teaching of this disclosure:

1. A positive-working lithographic printing plate precursor thatcomprises:

-   -   a grained and anodized aluminum-containing substrate,    -   a poly(vinyl phosphonic acid) interlayer disposed directly on        the grained and anodized aluminum substrate,    -   a first ink receptive layer that is disposed directly on the        poly(vinyl phosphonic acid) interlayer, the first ink receptive        layer comprising at least one water-insoluble, alkali        solution-soluble or -dispersible resin, and an aromatic acid dye        that comprises at least two aromatic groups and that is present        in an amount of least 0.5 weight %, based on the total dry        weight of the first receptive layer,    -   the positive-working lithographic printing plate precursor        further comprising an infrared radiation absorber in either the        first ink receptive layer or in an optional second ink receptive        layer that is disposed over the first ink receptive layer, or in        both of the first and second ink receptive layers.

2. The precursor of embodiment 1, wherein the aromatic acid dye comprisetwo or more carboxylate, sulfonate, phenolate, or phosphonate groups.

3. The precursor of embodiment 1 or 2, wherein the aromatic acid dye isselected from the group consisting of bis-azo dyes, tris-azo dyes,triphenyl methane dyes, and anthraquinone dyes.

4. The precursor of any of embodiments 1 to 3, wherein the aromatic aciddye is present in the first ink receptive layer in an amount of at least0.2 weight % and up to and including 10 weight %, based on the total dryweight of the first ink receptive layer.

5. The precursor of any of embodiments 1 to 4 comprising a grained and asulfuric acid anodized aluminum substrate.

6. The precursor of any of embodiments 1 to 5 that is a single-layerprecursor, wherein the first ink receptive layer is the only imageablelayer and which comprises the infrared radiation absorber in an amountof at least 0.5 weight %, based on the first ink receptive layer totaldry weight.

7. The precursor of any of embodiments 1 to 5 that is a double-layerprecursor comprising the second ink receptive layer disposed over thefirst ink receptive layer.

8. The precursor of embodiment 7, wherein only the second ink receptivelayer comprises the infrared radiation absorber.

9. The precursor of embodiment 7, wherein only the first ink receptivelayer comprises the infrared radiation absorber.

10. The precursor of embodiment 7, wherein the same or differentinfrared radiation absorber is in both of the first ink receptive layerand the second ink receptive layers.

11. The precursor of any of embodiments 1 to 10, wherein the first inkreceptive layer is substantially free of basic dyes having an absorptionpeak of at least 400 nm and up to and including 700 nm.

12. A method for forming a lithographic printing plate, comprising:

-   -   imagewise exposing the positive-working lithographic printing        plate precursor of any of embodiments 1 to 11 with infrared        radiation to form an imaged precursor comprising exposed regions        and non-exposed regions in the first ink receptive layer and the        second ink receptive layer, if present, and    -   processing the imaged precursor to remove the exposed regions of        the first ink receptive layer and of the second ink receptive        layer, if present.

13. The method of embodiment 12 comprising processing the imagedprecursor using a processing solution having a pH of at least 12 and upto and including 14.

14. The method of embodiment 12 or 13 comprising processing the imagedprecursor using a silicate-free processing solution having a pH of atleast 12.5 to and including 14.

15. The method of any of embodiments 12 to 14 comprising processing theimaged precursor using a silicate-free developer composition having a pHof at least 12 and comprising at least 0.001 gram-atom/kg of a metalcation M²⁺ selected from the group consisting of barium, calcium,strontium, and zinc cations.

16. The method of embodiment 15 wherein the metal cation M²⁺ is one ormore of calcium, strontium, and zinc cations, and is present in thedeveloper composition in an amount of at least 0.001 and up to andincluding 0.01 gram-atom/kg.

17. The method of any of embodiments 12 to 16 comprising processing theimaged precursor using a silicate-free developer composition furthercomprising a chelating agent that has a complex formation constant (logK) for the calcium or strontium M²⁺ metal cation of at least 3.5 andless than or equal to 4.5, and a log K for aluminum ion that is 7 orless.

The following Examples are provided to illustrate the practice of thisinvention and are not meant to be limiting in any manner. In theseExamples, the following materials were used (dyes are shown below at theend of the Examples.

BLO represents γ-butyrolactone. Byk ® 307 is a polyethoxylateddimethylpolysiloxane copolymer that is available from Byk Chemie(Wallingford CT). PM represents Dowanol ® PM. AC668 was a polymer madeusing methacrylamide-N-tetrazole, meth- acrylic acid, N-methoxy methylmethacrylamide, N-phenyl maleimide, and acrylonitrile at an18.5/4.2/13.9/21.0/42.4 weight % ratio. AC750 was a polymer made usingMAT/MAS/NPMI/Mam/AN/ NMMA 15.0/4.2/12.6/23.5/44.7/7.2 weight % ratiowith an acid number of 104 methacylamide-N-tetrazole, methacrylic acid,N- methoxy methyl, methacrylamide, N-phenyl maleimide, and acrylonitrileat a 15.0/4.2/12.6/23.5/44.7 weight % ratio. Substrate A was a 0.3 mmgauge aluminum sheet that had been electro- chemically grained andanodized having an R_(a) of 0.45 and had been subjected topost-treatment with poly(vinyl phosphonic acid). Substrate B was a 0.3mm gauge aluminum sheet that had been electro- chemically grained andanodized having an R_(a) surface value of 0.35 and had been subjected topost-treatment with poly(vinyl phosphonic acid). Solvent Mixture L20 isa solvent mixture of methyl ethyl ketone, PM, BLO, water, and Dioxalaneat a 45/20/10/10/15 weight ratio. Developer 400 xLo is a high pH (over12) silicate-free processing solution containing potassium hydroxide andsodium citrate as the primary components and small amounts ofsurfactants. Electra XD is a high run length thermal positive-workinglithographic printing plate precursor that is available from EastmanKodak Company. AC739 represents a polyurethane resin made usingdimethylolpropionic acid, 1,4-butanediol,4,4′-diphenylmethanediisocyanate and KF-6001 silicon (carbinol Shinetsu,Japan) at a weight ratio of 24/5.76/ 10.56/59.69. Resin B18 is apoly(vinyl acetal) with butyral and salicyldehyde groups. Resole BPA1100is a bis-phenol A resole available from Georgia Pacific. IR Dye A (TrumpDye) is represented by the following formula and can be obtained fromEastman Kodak Company (Rochester, NY).  

 

4-DMABA represents dimethyl aminobenzoic acid. Resole 9900LB is a resole(p-cresol/phenol) resin that is available from Momentive (Germany).Polyfox ® PF652 is a leveling agent that is available from Omnova(Germany). Violet 612 is available from Ludewig (Germany).

The following compounds have the noted structures:

CAS 4399-55-7 Direct Blue 71

Alizarin Blue black B CAS 1324-21-6

Naphthol blue black: CAS Number: 1064-48-8; anionic Bisaro dye

Eosin

Diamingrün

Trypanblau CAS 72-57-1

Crystal Violet CAS 548-62-9

Phloxine

Ethyl Violet CAS 2390-59-2

D11 Dye: Triarylmethane dye (CAS num- ber 433334-19-1) available fromPCAS (Longjumeau, France) repre- sented by the structure:

 

Sudan Black

Invention Examples 1-3 and Comparative Examples 1-4

Two-layer, positive-working lithographic printing plate precursors wereprepared as follows:

First ink receptive Layers A-F were prepared by coating a first inkreceptive layer formulation prepared by dissolving the components asshown below in TABLE I in 120 g of Solvent Mixture L20 onto a sample ofSubstrate A and drying at 80° C. for 2 minutes to provide a dry firstink receptive layer coating weight of 0.8 g/m².

Second ink receptive Layer A was prepared by coating a formulationprepared by dissolving 9.6 g of Resin B18, 6.69 g of Resole 9900LB, 0.42g of Trump Dye, 0.33 g of Violet 612, 0.33 g Sudan Black, 1.02 g of4-DMABA, 0.033 g of Byk® 307, and 1.64 AC739 in 380 g of a solventmixture made up of methyl ethyl ketone and Dowanol® PM (35:65 weightratio) on a sample of Substrate A and dried to provide a dry second inkreceptive layer coating weight of 0.7 g/m².

Second ink receptive Layer B was made by coating a formulation preparedby dissolving 10.46 g of Resin B18, 5.18 g of Resole BPA1100, 0.32 g ofTrump Dye, 0.52 g of Violet 612, 0.32 g of 4-DMABA, and 0.03 g of Byk®307 in 143 g of a solvent mixture made up of methyl ethyl ketone andDowanol® PM (35:65 weight ratio) on a sample of Substrate A to obtain adry second ink receptive layer coating weight of 0.7 g/m².

Second ink receptive Layer C was made by coating a formulation preparedby dissolving 1.30 g of Resin B18, 1.25 g of Resole 9900LB, 0.051 g ofTrump Dye, 0.041 g of Violet 612, 0.041 g of Sudan Black, 0.04 g of Byk®307 in 47 g of a solvent mixture made up of methyl ethyl ketone andDowanol® PM (35:65 weight ratio) on a sample of Substrate A to obtain adry second ink receptive layer coating weight of 0.7 g/m².

The two-layer lithographic printing plate precursors in InventionExamples 1-3 and Comparative Examples 1-4 were obtained by applying thevarious second ink receptive layer on the first ink receptive layers asindicated below in TABLE I, and drying using conventional conditions.

TABLE I Invention Invention Invention Comparative Invention ComparativeComparative Comparative Example 1 Example 2 Example 3 Example 1 Example4 Example 2 Example 3 Example 4 First Ink Layer A Layer A Layer B LayerC Layer A Layer D Layer E Layer F Receptive Layer AC668 0 0 9.78 9.78 09.78 9.78 9.78 AC750 9.78 9.78 0 0 9.78 0 0 0 Naphthol 0.2 0.2 0 0 0.2 00 0 Blue Black Eosin 0 0 0.2 0 0 0 0 0 Dye D11 0 0 0 0.2 0 0 0 0 AcidViolet 0 0 0 0 0 0.2 0 0 Phloxine 0 0 0 0 0 0 0.2 0 Ethyl violet 0 0 0 00 0 0 0.2 Byk ® 307 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 (10% in PM)N-benzyl- 0 0 0 0.1 0 0 0 0 chinolinium bromide Second Ink Layer A LayerB Layer A Layer B Layer C Layer A Layer A Layer A Receptive Layer

The resulting two-layer positive-working lithographic printing plateprecursors were conditioned for 2 days at 60° C. After 1 day at roomtemperature, an evaluation was carried out processing each precursorusing a Mercury Mark 6 processor and Developer 400 xLo at 1500 mm/minprocessing speed and 23° C.

Performance Evaluation:

Photospeed (Clear Point/Linear Point):

To assess the photospeed, each lithographic printing plate precursor wasimaged with test patterns comprising solids and 8×8 checkerboard at 4 Wto 16 W in 1 W steps at 360 rpm using a Creo Quantum 800 imagesetter(from 39 mJ/cm² to 102 mJ/cm²). The imaged precursors were thenevaluated for clear point and linear point (50% of 8×8 to give 50% withSpectroPlate from Techkon). “Clear point” is the exposure energy atwhich no coating residue is visible with the unaided eye. The dot sizeof the 8×8 pixels is measured with SpectroPlate from Techkon. “Linearpoint” is the energy setting giving a 50% reading as extrapolated.

Staining (ΔE):

The ΔE was used as a measure for staining. A drop of the Solvent MixtureLM 20 was placed in a spot of a non-image area and ΔE (color differencebetween within and outside the spot) was measured using an X-Ritedensitometer. The results of the performance evaluations are summarizedbelow in TABLE IA. The level of staining was considered negligible whenthe ΔE was <0.15.

“Blanket Toning” refers to the effect where the non-imaged regions thatare supposed to be hydrophilic and lithographic printing ink-repellant,become more lithographic printing ink receptive and thereby transferlithographic printing ink to the blanket roller on a printing press. Asthis build-up on the blanket roller becomes stronger, at some point thelithographic printing ink is transferred from the blanket roller topaper copies to cause a dirty background in the non-imaged regions onthe printed copies, which is then referred to as “Toning on Paper”.

TABLE IA Invention Invention Invention Comparative Invention ComparativeComparative Comparative Example 1 Example 2 Example 3 Example 1 Example4 Example 2 Example 3 Example 4 Clear Point 50 50 50 40 80 50 50 40(mJ/cm²) Linear Point 100 90 50 66 121 53 50 59 (mJ/cm²) ΔE 0.05 0.050.07 0.05 0.08 0.89 0.9 1.1 Blanket None None None Slight None High HighHigh Toning Toning on None None None Slight None High High High Paper

The results shown in TABLE IA indicate that only Naphthol blue black andEosin in the first ink receptive layer provided precursors that werefree of staining after development. While triphenylmethane dyes such asEthyl Violet, D11 and Acid violet provided very good contrast, they alsocaused high staining after development was carried out with the silicatefree high pH developer. Eosin, which is similar to the triphenylmethanedyes, provided both good contrast and no staining because it carriesacidic groups on each aryl unit.

Invention Examples 4-7 and Comparative Examples 5 and 6

Positive working, single-layer lithographic printing plate precursorsfor Invention 4-7 and Comparative Example 5 were prepared by coating afirst ink receptive layer formulation using the components (in grams)shown below in TABLE II dissolved in a solvent mixture of methyl ethylketone and Dowanol® PM (35:65 weight ratio) onto a sample of Substrate Ato obtain a dry first ink receptive layer coating weight of 1.3 g/m².Similarly, in Comparative Example 6, the formulation described inExample 4 of U.S. Pat. No. 6,255,033 (Levanon et al.) was applied to asample of Substrate A to provide a dry coating weight of 1.3 g/m².

TABLE II Invention Invention Comparative Invention Example 5 InventionExample 7 Example 5 Example 4 Direct Example 6 Alizarin Crystal DyeDiamingrün Blue 71 Trypanblau Blue black B Violet Resin B18 2.61 2.612.61 2.61 2.61 Resole BPA 1100 1.30 1.30 1.30 1.30 1.30 Trump Dye 0.080.08 0.08 0.08 0.08 4-DMABA 0.08 0.08 0.08 0.08 0.08 Polyfox^( ®) PF 6520.02 0.02 0.02 0.02 0.02 Contrast Dye 0.13 0.13 0.13 0.13 0.13 SolventMixture 35.78 35.78 35.78 35.78 35.78

The single-layer positive-working lithographic printing plate precursorwas then conditioned for 2 days at 60° C.

Performance Evaluation:

To assess the photospeed, each precursor was imaged with test patternscomprising solids and 8×8 checker board using a Creo Quantum 800imagesetter at energies between 50 mJ/cm² to 120 mJ/cm². The imagedprecursors were then developed using a Mercury Mk6 processor andDeveloper 400 xLo at 2000 mm/minute processing speed and 21° C.

Each lithographic printing plate was evaluated for clear point andlinear point (both defined above).

Staining (ΔE):

The level of staining of the non image area in each lithographicprinting plate was measured using ΔE. This was done by placing a drop ofthe solvent mixture Dowanol® PM/MEK (1:1 weight ratio) in a spot of anon-image area at the exposure energy at linear point, and ΔE (the colordifference between within and outside the spot) was measured using anX-Rite densitometer. The level of staining was considered negligiblewhen the ΔE was <0.15.

The results of the performance evaluation are summarized below in belowTABLE IIA.

TABLE IIA Invention Invention Invention Invention ComparativeComparative Example 4 Example 5 Example 6 Example 7 Example 5 Example 6Clear point (mJ/cm²) 70 70 70 70 70 70 Linear Point (mJ/cm²) 138 127 125132 123 123 ΔE 0.09 0.09 0.11 0.1 >1 >1 Blanket Toning None None NoneNone High High Toning on Paper None None None None High High

The results shown in TABLE IIA indicate that only the aromatic acid dyesused in Invention Examples 4-7 provided no staining. The toningevaluation was made by printing up to 10,000 copies. As noted in TABLESIA and IIA, all lithographic printing plates that exhibited a ΔEof >0.15 showed either blanket toning, toning on paper, or both.

Press Test:

The contrast dyes used according to the present invention (for example,Naphthol blue black) provided strong contrast as desired without causingundesirable staining from imaged positive-working lithographic printingplate precursors that comprised a substrate that had been post-treatedwith poly(vinyl phosphonic acid) and were developed with a high pH,silicate-free processing solution (for example, Developer 400 xLo).Without being limited to a particular mechanism, it is believed thatthis unexpected property is provided by the high concentration ofsolubilizing groups in the contrast dyes, which solubilizing groupsimprove their solubility in the processing solution but which have alower tendency to adhere to the poly(vinyl phosphonic acid) interlayeron the substrate.

It was found that this unexpected result was achieved with bothsingle-layer and double-layer positive-working lithographic printingplate precursors.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

The invention claimed is:
 1. A method for forming a lithographicprinting plate, comprising: imagewise exposing a positive-workinglithographic printing plate precursor with infrared radiation to form animaged precursor comprising exposed regions and non-exposed regions in afirst ink receptive layer and a second ink receptive layer, if present,and processing the imaged precursor to remove the exposed regions of thefirst ink receptive layer and of the second ink receptive layer, ifpresent, using a silicate-free processing solution having a pH of atleast 12 and up to and including 14 and comprising at least 0.001gram-atom/kg of a metal cation M²⁺ selected from the group consisting ofbarium, calcium, strontium, and zinc cations; the positive-workinglithographic printing plate precursor comprising a grained and anodizedaluminum-containing substrate, a poly(vinyl phosphonic acid) interlayerdisposed directly on the grained and anodized aluminum-containingsubstrate, a first ink receptive layer that is disposed directly on thepoly(vinyl phosphonic acid) interlayer, the first ink receptive layercomprising at least one water-insoluble, alkali solution-soluble or-dispersible resin, and an aromatic acid dye that is Naphthol blueblack, Trypanblau, Direct Blue 71, or Diamingrün having the structuresshown below, the aromatic acid dye being present in an amount of atleast 0.5 weight %, based on the total dry weight of the first inkreceptive layer, the positive-working lithographic printing plateprecursor being infrared radiation-sensitive and further comprising aninfrared radiation absorber in either the first ink receptive layer orin an optional second ink receptive layer that is disposed over thefirst ink receptive layer, or in both of the first and the second inkreceptive layers, Direct Blue 71

Naphthol blue black

Diamingrün

Trypanblau


2. The method of claim 1 comprising imagewise exposing thepositive-working lithographic printing plate precursor comprising thefirst ink receptive layer and no second ink receptive layer.
 3. Themethod of claim 1, comprising imagewise exposing the positive-workinglithographic printing plate precursor comprising a second ink receptivelayer over the first ink receptive layer.
 4. The method of claim 1wherein the metal cation M²⁺ is one or more of calcium, strontium, andzinc cations, and is present in the silicate-free processing solution inan amount of at least 0.001 and up to and including 0.01 gram-atom/kg.5. The method of claim 1, wherein the silicate-free processing solutionfurther comprises a chelating agent that has a complex formationconstant (log K) for calcium or strontium M²⁺ metal cation of at least3.5 and less than or equal to 4.5, and a log K for aluminum ion that is7 or less.
 6. The method of claim 1, wherein the grained and anodizedaluminum-containing substrate is a grained and a sulfuric acid anodizedaluminum-containing substrate.
 7. The method of claim 2, wherein thefirst ink receptive layer in the positive-working lithographic printingplate precursor comprises the infrared radiation absorber in an amountof at least 0.5 weight %, based on the first ink receptive layer totaldry weight.
 8. The method of claim 3, wherein only the second inkreceptive layer in the positive-working lithographic printing plateprecursor comprises the infrared radiation absorber.
 9. The method ofclaim 3, wherein only the first ink receptive layer in thepositive-working lithographic printing plate precursor comprises theinfrared radiation absorber.
 10. The method of claim 3, wherein the sameor different infrared radiation absorber is in both of the first inkreceptive layer and the second ink receptive layers of thepositive-working lithographic printing plate precursor.
 11. The methodof claim 1, wherein the first ink receptive layer of thepositive-working lithographic printing plate precursor comprises lessthan 0.1 weight %, based on the total dry weight of the first inkreceptive layer, of basic dyes having an absorption peak of at least 400nm and up to and including 700 nm.
 12. A method for forming alithographic printing plate, comprising: imagewise exposing apositive-working lithographic printing plate precursor with infraredradiation to form an imaged precursor comprising exposed regions andnon-exposed regions in a first ink receptive layer and a second inkreceptive layer, if present, and processing the imaged precursor toremove the exposed regions of the first ink receptive layer and of thesecond ink receptive layer, if present, using a silicate-free processingsolution having a pH of at least 12 and up to and including 14 andcomprising at least 0.001 gram-atom/kg of a metal cation M²⁺ selectedfrom the group consisting of barium, calcium, strontium, and zinccations; the positive-working lithographic printing plate precursorcomprising a grained and anodized aluminum-containing substrate, apoly(vinyl phosphonic acid) interlayer disposed directly on the grainedand anodized aluminum-containing substrate, a first ink receptive layerthat is disposed directly on the poly(vinyl phosphonic acid) interlayer,the first ink receptive layer comprising at least one water-insoluble,alkali solution-soluble or -dispersible resin, and an aromatic acid dyethat is Naphthol blue black that is present in an amount of at least 0.5weight %, based on the total dry weight of the first ink receptivelayer, the positive-working lithographic printing plate precursor beinginfrared radiation-sensitive and further comprising an infraredradiation absorber in either the first ink receptive layer or in anoptional second ink receptive layer that is disposed over the first inkreceptive layer, or in both of the first and the second ink receptivelayers.